a US guy just challenged me and i was wondering if its possible to make a "ping" feature available. additionally (or alternatively) a list of preferred servers in the profile would be a better solution than just the country flags.

You mean a ping display like the one on the score board?
Well a flag is for sure much easier to code then a server selection.. and i think green will not spend much more time on programming the ladder.

it can be an interesting idea but I wouldn't implement it as esteel already mentioned.

People should know, that, when being challenged by someone who is too far away geographically, declining the challenge is the best thing to do. If you live in Europe and get challenged by an American you shouldn't accept, unless you know what you do and you're willing to play a choppy and laggy match (however, there are people who like that, or who have barely a choice, like Americans since there aren't many registered Americans in the ladder)